This invention relates to a borate-containing composition which can be effective as a catalyst for hydrogenating aromatic hydrocarbons, to a process for producing the composition, and to a process for using the composition.
In an alkylation process, complex saturated hydrocarbon molecules are formed by direct union of a saturated hydrocarbon molecule and an unsaturated hydrocarbon molecule. For example, light compounds such as isobutane and butylene are converted into heavier compounds through the control of temperature and pressure in the presence of an acid catalyst. Hydrofluoric acid is presently widely used as an alkylation catalyst.
Some undesirable aromatic compounds such as, for example, heavily substituted aromatic compounds, wherein each of the alkyl groups has about 3 to about 9 carbon atoms per alkyl group, are also produced in an alkylation process. When the alkylation products are used in household products, food-related applications, cosmetics, and lantern fuel, it is generally required that they be substantially free of any aromatic compounds. The concentration of aromatic compounds can generally be reduced to 0.03 weight % or higher by a hydrotreatment process using commercially available nickel catalysts. However, reduction of aromatic compounds to less than 0.03 weight % by such hydrotreatment has never been achieved with commercially available catalysts. Therefore, a more active catalyst is required to substantially reduce the content of aromatic compounds, especially from the heavy end of the alkylate fraction. It is also highly desirable to develop a new catalyst that can substantially reduce the concentration of the undesirable aromatic compounds.
Furthermore, sulfur or sulfur-containing compounds may be present in refining processes and potentially could be present in an alkylation process. Commercially available catalysts used in removing or reducing the aromatic compounds are normally prone to sulfur poisoning. Therefore, it appears there is an ever-increasing need to develop a catalyst which is not sensitive to sulfur or sulfur-containing compounds and still can substantially reduce the concentration of the undesirable aromatic compounds.
An object of this invention is to provide a metal borate-containing composition. Also an object of this invention is to provide a process for producing this composition. Another object of this invention is to employ this composition in a process for hydrogenating aromatic hydrocarbons which are present in a hydrocarbon-containing fluid. An advantage of the invention is that the aromatic hydrocarbons content can be substantially reduced. Other objects will become apparent from the detailed description and the appended claims.
According to a first embodiment of this invention, a composition is provided which comprises an inorganic support having incorporated therein a hydrogenation catalyst wherein the support comprises aluminum, zirconium, and borate.
According to a second embodiment of this invention, a process is provided which comprises: (1) contacting an aluminum salt, a zirconium salt, and an acidic boron compound under a condition sufficient to effect the production of a solid inorganic support material comprising aluminum, zirconium, and borate; and (2) combining the support with a hydrogenation catalyst precursor.
According to a third embodiment of this invention, a process which can be used for catalytically hydrogenating an aromatic compound with hydrogen to a more saturated hydrocarbon is provided. The process comprises contacting a hydrocarbon-containing fluid which contains an aromatic compound, in the presence of a catalyst, with hydrogen under a condition effective to substantially hydrogenate the aromatic compound to a saturated compound.
According to the first embodiment of the invention, the hydrogenation catalyst of the composition of this invention can be any hydrogenation catalyst known to one skilled in the art. Preferably, such catalyst is one of the Group VIII metals, Group VIII metal-containing compounds, or combinations of two or more thereof. The term xe2x80x9cGroup VIIIxe2x80x9d refers to the Periodic Table of the Elements, CRC Handbook of Chemistry and Physics, 67th edition, 1986-1987, CRC Press, Boca Raton, Fla. The presently preferred hydrogenation catalyst is platinum or a platinum compound such as platinum oxide.
The support component of the composition of this invention comprises, consists essentially of, or consists of, aluminum, zirconium, and borate. Aluminum and zirconium in the composition are generally not in the metal form. Preferably the support material comprises, consists essentially of, or consists of aluminum borate and zirconium borate. More preferably the support material comprises, consists essentially of, or consists of a zirconium/aluminum/borate composite.
Generally, the component has a weight ratio of Al to Zr in the range of from about 0.1:1 to about 30:1, preferably about 1:1 to about 20:1, and most preferably about 4:1 to about 12:1 and a weight ratio of (Al+Zr) to B in the range of from about 0.1:1 to about 10:1, preferably about 1:1 to about 6:1, and most preferably about 1.5:1 to about 3:1. Generally, the support component has a surface area, measured by the BET method employing N2, of about 200 to about 400 m2/g and a pore volume, measured by a pore size distribution method employing N2, of about 0.2-1.5 cc/g. It can have any suitable shape such as spherical, cylindrical, trilobal or irregular, or combinations of two or more thereof. It also can have any suitable particle size. The presently preferred size is about 0.4 to about 0.8 mm. If particles of the support component have been compacted and extruded, the formed cylindrical extrudates generally have a diameter of about 1 to about 4 mm and a length of about 3 to about 10 mm. It is within the scope of this invention to have minor amounts of aluminum oxide and zirconium oxide, generally about 1 to about 5 weight % of each, present in the support component. The hydrogenation catalyst component of the composition can be present in the composition of this invention in any quantity as long as that quantity can effect the substantial reduction of aromatic compound concentration in the product stream of an alkylation reaction. Generally, the weight % of the hydrogenation catalyst component in the invention composition can be in the range of from about 0.01 to about 50, preferably about 0.05 to about 25, and most preferably 0.1 to 15.
Preferably, the inorganic support component is prepared by a method comprising coprecipitation. A first aqueous solution containing any water-soluble aluminum salt such as, for example, aluminum nitrate; any water-soluble zirconium salt such as, for example, zirconyl nitrate; and any water-soluble acidic boron compound (preferably a boric acid, more preferably H3BO3) is prepared. Any suitable concentrations of these compounds in the aqueous solution can be employed so long as the concentration can result in the production of the inorganic support component disclosed above. Generally about 0.02 to about 1 mole/l of each compound, depending on the desired Al:Zr:B ratio can be employed. The initial pH of this aqueous solution is generally about 1 to about 3.
An aqueous alkaline solution, preferably an aqueous solution of ammonia containing about 25 to about 28 weight % NH3, generally having a pH of about 10 to about 14, is then added to the first aqueous solution in an amount sufficient to raise the pH of the first solution to 7 or above 7, preferably to about 8-9, to afford the coprecipitation of borates of aluminum and zirconium.
The dispersion of the formed coprecipitate in the aqueous solution is then subjected to any suitable solid-liquid separation methods known to one skilled in the art such as, for example, filtration to substantially separate the coprecipitate from the aqueous solution. Preferably, the coprecipitate is washed with water to remove adhered solution therefrom, optionally followed by washing with a water-soluble organic solvent such as methanol, ethanol, isopropanol, acetone, or combinations of two or more thereof. The presently preferred solvent is isopropanol. The washed coprecipitate is generally dried by any methods known to one skilled in the art. The presently preferred drying is in a vacuum oven, under any pressure, at a temperature of about 110 to about 180xc2x0 C. for about 2 to about 16 hours.
The dried solid is then calcined by any methods known to one skilled in the art. Generally calcination can be done in air, at a temperature of about 300 to about 1000xc2x0 C., preferably about 350 to about 750xc2x0 C., and most preferably 450 to 600xc2x0 C., for about 1 to about 16 hours. It is within the scope of this invention to mix the formed coprecipitate with a carbon-containing binder material, such as a polyglycol, a polyoxazoline or carbon black, which is substantially burned off during the calcining step, and/or with an inorganic binder material such as, for example, alumina, colloidal alumina, clay, calcium aluminate, water glass or combinations of two or more thereof. It is also within the scope of this invention to extrude or pelletize or tablet the coprecipitate, with or without a binder, before the calcination.
The hydrogenation catalyst component of this invention can be combined with the support component in any suitable manner so long as the composition of this invention can be prepared. Generally, the support component is first impregnated with at least one dissolved hydrogenation catalyst compound such as by incipient wetness impregnation. The support component can also be sprayed with an impregnating solution containing at least one dissolved hydrogenation catalyst compound. Generally, the concentration of the hydrogenation catalyst compound in the impregnating solution is in the range of from about 0.1 to about 5 mol/l, preferably about 0.2 to about 2 mol/l. Preferably, the solvent of the impregnating solution is water or an alcohol such as ethanol or mixtures thereof. Suitable hydrogenation catalyst compounds which can be used to impregnate the support component include, but are not limited to, chloroplatinic acid, tetramine platinum hydroxide hydrate, platinum chloride, platinum bromide, platinum iodide, tetramine platinum nitrate, tetrachlorodiamine platinum, tetrakis (triphenylphosphine phosphine) platinum, platinum oxide, palladium acetate, palladium sulfate, palladium chloride, tetrapalladium sulfate, palladium nitrate, palladium diaminonitrile, nickel chloride, nickel nitrate, nickel sulfate, ammonium nickel sulfate, nickel acetate, nickel oxalate, hexamminenickel chloride, hexamminenickel nitrate, hexamminenickel sulfate, other coordination compounds of divalent nickel, rhenium oxides (such as Re2O7), rhenic acid (H2ReO4), perrhenic acid (HReO4), alkali metal rhenates (such as Na2ReO4), alkali metal perrhenates (such as NaReO4), ammonium rhenate, ammonium perrhenate, or combinations of two or more thereof. It should be noted that the metal of the hydrogenation catalyst compounds can have any available oxidation states. For example, platinum can have the oxidation state of 0, 2, 4, or combinations of two or more thereof. The presently preferred hydrogenation catalyst compound is chloroplatinic acid (H2PtCl6.6H2O).
If it is desired to impregnate the inorganic support component additionally with at least one second hydrogenation catalyst such as, for example, a rhenium compound, this can be done before or concurrently with or after the impregnation with the first hydrogenation catalyst compound. The concentration of the second hydrogenation catalyst compound in the impregnating solution generally can be within the range disclosed above for the hydrogenation catalyst compound. The solvent of this impregnating solution can also be water and/or an alcohol, such as ethanol, or any other suitable liquid in which the particular second hydrogenation catalyst compound is soluble and stable.
The weight ratio of the hydrogenation catalyst-impregnating solution to the inorganic support component can be any ratio that can produce the composition disclosed in the first embodiment of this invention. Generally the weight ratio can be such as to attain a weight percentage of about 0.01 to about 50, preferably about 0.05 to about 25, and more preferably about 0.1 to about 15 weight % hydrogenation catalyst, on an elemental basis, in the finished composition, i.e., the composition obtained in the last step of the preparation method of this invention, as disclosed above. If impregnation with the second hydrogenation catalyst compound is also carried out, the weight ratio of the other hydrogenation catalyst-containing impregnating solution to the support component generally is such as to attain a weight percentage of about 0.01 to about 10, preferably about 0.05 to about 8, weight % the other hydrogenation catalyst, on an elemental basis, in the finished composition.
The hydrogenation catalyst-impregnated composition generally is dried at a temperature of about 5 to about 150xc2x0 C. and then calcined under a condition which can be the same, or substantially the same, as the calcination of the support component disclosed above. The calcining step can be done in an inert atmosphere, i.e., in the presence of N2, He, Ne, Ar, or combinations of two or more thereof. The calcining step can also be done in an O2-containing atmosphere (e.g., air).
Before its use as a hydrogenation catalyst, the obtained calcined composition generally is treated with a reducing agent to reduce the oxidation state of the hydrogenation catalyst compound. The reducing agent is preferably a gas stream which comprises, or essentially of, hydrogen. The treatment can be carried out generally at a temperature of about 200 to about 550xc2x0 C., preferably about 350 to about 450xc2x0 C., for a time period of about 0.5 to about 10 hours. Other examples of reducing agents include, but are not limited to, carbon monoxide, C1-C6 alkanes, and C2-C6 alkenes, C4-C6 alkadienes, or combinations of two or more thereof.
The composition of this invention can be used in a variety of catalytic applications. In the third embodiment of this invention the composition is employed as a catalyst for hydrogenating aromatic hydrocarbons with a hydrogen-containing fluid, or hydrogen, to non-aromatic or more saturated hydrocarbons, such as alkenes, alkanes, cycloalkenes, cycloalkanes, or combinations of two or more thereof. Any aromatic compounds can be employed as feed. Examples of suitable feed aromatic hydrocarbons which can be hydrogenated generally contain 6 to about 30, preferably about 6 to about 25, and most preferably 6 to 20 carbon atoms per molecule and include, but are not limited to, benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, trimethylbenzenes, tetramethylbenzenes, pentamethylbenzene, hexamethylbenzenes, methylethylbenzenes, ethyl-substituted benzenes, n-propyl-substituted benzenes, isopropyl-substituted benzenes, n-butyl-substituted benzenes, isobutyl-substituted benzenes, t-butyl-substituted benzenes, naphthalene, or combinations of two or more thereof.
The term xe2x80x9cfluidxe2x80x9d used herein refers to gas, vapor, liquid, or combinations of two or more thereof. The term xe2x80x9cmore saturated hydrocarbonxe2x80x9d refers to non-aromatic hydrocarbon(s).
In a preferred application, a hydrocarbon feed stream comprises at least one aromatic hydrocarbon as a minor component, i.e., less than about 50 weight %, preferably about 0.1 to about 10 weight %, and most preferably less than 5 weight %, of the feed. The feed stream can also comprise a sulfur compound in minor content. When a sulfur compound is present in the feed stream, it is preferred the concentration of sulfur compound is less than about 1 weight %, preferably less than about 0.1 weight %, more preferably less than 0.05, and most preferably less than 0.01 weight % of sulfur. Any sulfur-containing compounds that are associated with a refining process can be present in the feed stream. Examples of sulfur compounds include, but are not limited to, thiophenes, thiophanes, thiophenols, sulfides, disulfides, mercaptans, mercaptides, and combinations of two or more thereof. The sulfur compounds commonly present in alkylation process are thiophenes such as benzo[b]thiophene, methylbenzolthiophene, dibenzothiophene, methyldibenzothiophene, and combinations of two or more thereof.
Generally, the feed stream comprises at least one alkane which can be straight chain or branched. Generally, the alkane can contain about 3 to about 30, preferably 6 to about 25, and most preferably 8 to 20 carbon atoms per molecule and is the major portion. In other words alkane or alkanes are present in the feed stream more than about 50 weight %, preferably more than 80 weight %, more preferably more than about 90 weight %, and most preferably more than 95 weight % of the feed.
According to the invention, a preferred feedstock is a product prepared by an alkylation process which can be further refined to a product that can be used as a specialty solvent such as that marketed under the tradename xe2x80x9cSoltrol(copyright) Solvent xe2x80x9d by Phillips Petroleum Company, Bartleville, Okla. The presence of aromatic hydrocarbons in this type of feedstock is undesirable, and can be removed by the hydrogenation process of this invention employing the catalyst composition of this invention. The alkylation process is well known to one skilled in the art and, for the interest of brevity, the description of which is omitted herein.
The process of the third embodiment of this invention can be carried out under any suitable condition which can substantially reduce the concentration of the aromatic compounds in the feed stream. The concentration of aromatic compounds is desirably reduced to less than about 0.1, more preferably to less than about 0.05, and most preferably to less than 0.03 weight %. Generally, the conditions can include a reaction temperature of about 10 to about 300xc2x0 C., preferably about 125 to about 200xc2x0 C., and most preferably 150 to 200xc2x0 C., a reaction pressure that can accommodate the temperatures and generally in the range of about 300 to about 750 psig, preferably about 400 to about 500 psig, a liquid hourly space velocity of the hydrocarbon feed stream (cc liquid feed per cc catalyst per hour) of about 1 to about 5 cc/cc/hour, preferably about 1.5 to about 3 cc/cc/hour, and a gas hourly space velocity of hydrogen gas of about 100 to about 500 cc/cc catalyst/hour preferably about 150 to about 300 cc/cc/hour. The amount of H2 in a hydrogen-containing fluid should be sufficient to hydrogenate essentially all aromatic hydrocarbons to saturated hydrocarbons. Generally, the aromatic hydrocarbon-containing feed stream is passed, together with a hydrogen-containing fluid, through a catalyst bed, either a fixed or a fluidized catalyst bed, containing the composition of this invention as the catalyst.
The hydrogenated product which exits the hydrogenation zone can undergo any desired separation such as, for example, distillation or a series of separations to obtain various purified product streams, primarily an alkane stream from which aromatic hydrocarbons have been substantially removed by the hydrogenation process of the third embodiment of this invention. The product of this hydrogenation process frequently is a mixture of alkanes and cycloalkanes, and each product component can be recovered from the hydrogenation product by any suitable, effective separation means known to one skilled in the art.